In a multi-carrier communication system such as an Orthogonal Frequency Division Multiple Access (OFDMA) system, the communicated signal consists of multiple subcarriers (also termed “tones”) that are transformed through a certain type of linear transformation (e.g., an inverse Fourier transform) into time signals. One of the distinctive characteristics of a multi-carrier signal in the time domain is that its peak-to-average-power ratio (PAPR) is undesirably high. To transmit a high-PAPR signal without significantly distorting its integrity, the transmitter circuitry has to operate in a linear region, which is normally realized by ensuring the average output signal level of the power amplifier (PA) lower than the PA's 1-dB compression point by a large amount, a process called “back-off”. There are some drawbacks for back-off. For example, the PA operates at a low efficiency, thereby consuming a significant amount of power. This is especially undesirable for a device that has a limited power supply.
To increase the transmission efficiency, thereby lowering the power consumption, one has to address the root of the problem, which is the high level of PAPR.